This invention relates to a method and apparatus for processing a substrate by use of plasma, and particularly to a technique that is suitable for a microwave plasma CVD apparatus for forming a thin film on a substrate to enhance performance in terms of operational efficiency and ease of maintenance.
A conventional microwave plasma processing apparatus is designed to clean up its interior, after a plasma-based process such as thin film formation, by application of a high-frequency electric field to the internal wall of the vacuum chamber in which the substrate has been processed so that deposits on the wall surface are etched off, as described in Japanese patent publications JP-A-1-231320, JP-A-1-231321, JP-A-1-231322, and JP-A-1-231323.
However, the above-mentioned conventional method is solely intended to clean up the vacuum chamber internal wall through application of the high-frequency electric field, and it does not consider the cleaning of places around the substrate holder where cleaning is most imperative. Moreover, the frequency of the applied electric field is not optimized and therefore the cleaning effect is not satisfactory. Another problem is that the cleaning operation promotes the sputtering of the internal wall surface, thereby spreading metallic contamination. A further problem is that for safety purposes, an expensive insulation structure is required for the chamber wall that functions as an electrode.